Don't set $env:TEMP on unix, instead use /tmp as workingdir for tests

lib/unix.ps1

@@ -13,7 +13,6 @@ if(!(is_unix)) {
 $scoopdir = $env:SCOOP, (Join-Path $env:HOME "scoop") | select -first 1
 $globaldir = $env:SCOOP_GLOBAL, "/usr/local/scoop" | select -first 1
 $cachedir = $env:SCOOP_CACHE, (Join-Path $scoopdir "cache") | select -first 1
-$env:TEMP = "/tmp"
 
 # core.ps1
 function ensure($dir) {

test/Scoop-TestLib.ps1

@@ -73,7 +73,12 @@ function setup_working($name) {
     }
 
     # reset working dir
-    $working_dir = "$env:TEMP/ScoopTestFixtures/$name"
+    if($PSVersionTable.Platform -eq 'Unix') {
+        $working_dir = "/tmp/ScoopTestFixtures/$name"
+    } else {
+        $working_dir = "$env:TEMP/ScoopTestFixtures/$name"
+    }
+
     if(test-path $working_dir) {
         Remove-Item -Recurse -Force $working_dir
     }